Nonwoven fabrics and binders therefor

ABSTRACT

Nonwoven fabrics that have excellent wet strength and dry strength are formed by adding to an aqueous suspension of natural and/or synthetic fibers a binder comprising (a) an anionic polymer latex and (b) a mixture of alkali metal salts of disproportionated rosin and fortified rosin, precipitating the binder on the fibers, and forming the treated fibers into a nonwoven fabric.

United States Patent Wilhelmi Feb. 22, 1972 [54] NONWOVEN FABRICS ANDBINDERS THEREFOR [72] Inventor: Werner Alfred Wilhelmi, Bussum,Netherlands [73] Assignee: Nederlandsche Bewoid Maatschappii N.V.

[22] Filed: Apr. 8, 1969 [21] Appl. No.2 814,456

[52] US. CL ..260/26, 117/140 A, 117/161 K, ll7/l6l KP, 117/161 P,117/161 UB, 117/161 UF,

117/168, 260/24, 260/27 R, 260/27 BB [51] Int. Cl ..'.C08d 9/12,C08g17/16,D06n 3/04 [58] Field of Search ..260/24, 26, 27; 117/140 A[56] References Cited UNITED STATES PATENTS 3,380,851 4/1968 Lindemannet al. ..1 17/140 Maruta ..162/168 3,451,890 6/1969 Stump 162/1683,490,937 1/1970 PletSCh ....1 17/63 3,510,344 5/1970 Dunderdale....l17/76 Primary Examiner-Hosea E. Taylor Assistant ExaminerRonald W.Grifi'm Att0mey-Daniel J. Reardon, Saul R. Bresch, George E. Lilly andEvelyn Berlow ABSTRACT 14 Claims, N0 Drawings NON WOVEN FABRICS ANDBINDERS THEREFOR This invention relates to nonwoven fabrics and to amethod for their production. It further relates to adhesive binders thatare used in the production of nonwoven fabrics.

Nonwoven fabrics are composed of loosely assembled webs of naturaland/or synthetic fibers that are bound together with an adhesive binder.Two general procedures are used commercially for the production ofnonwoven fabrics. In the dry process" a web of fibers, which is formed,for example, by carding or garnetting, is impregnated with a binder, andthe treated web is then dried. In the wet process, an aqueous suspensionof the fibers is formed, a binder is added to the aqueous suspension andprecipitated on the fibers, and the treated fibers are formed into a matusing papermaking equipment, such as fourdriniers or Rotoformers. Formany applications, the wet process of producing nonwoven fabrics ispreferred over the dry process because it yields superior products andbecause it permits higher production rates. Because the fibers aredeposited with three-dimensional random orientation, the products of thewet process have equal strength in all directions, whereas in theproducts of the dry process the fibers are ordinarily oriented parallelto the machine direction. In addition, the products of the wet processare stronger and more uniform throughout the fiber mat because thebinder is applied uniformly to the fibers in the aqueous suspension.

A number of polymers have been proposed as binding agents for nonwovenfabrics. Among them are acrylic resins, styrene-butadiene, copolymers,polyurethane, polyesters, polyamides, polyvinyl acetate, polyvinylchloride, chlorinated polypropylene, and synthetic and natural rubber.None of these binders has given entirely satisfactory results when usedin the production of nonwoven fabrics by the wet process because thepolymers are not adequately retained on the fibers and the productsproduced do not have the desired combination of properties, andparticularly good wet strength and dry strength.

in accordance with this invention, it has been found that nonwovenfabrics that are characterized by excellent tensile strength, softness,flexibility, and other valuable properties result when the binder usedin the aforementioned wet process comprises a polymer latex and amixture of alkali metal salts of disproportionated rosin and fortifiedrosin. The properties of nonwoven fabrics prepared using the novelbinders of this invention are in many ways superior to those of nonwovenfabrics prepared from binders that do not contain the mixture ofmodified rosin salts. Of particular importance is the higher tensilestrength of the products ofthis invention.

Nonwoven fabrics are prepared in accordance with the process of thisinvention by forming a dilute aqueous suspension of fibers, adding tothe suspension and precipitating on the fibers in the suspension abinder comprising a polymer and a mixture of alkali metal salts ofdisproportionated rosin and fortified rosin, forming the treated fibersinto a nonwoven fabric, and drying the fabric.

Any of the natural fibers and synthetic fibers that are commonly used inthe production of nonwoven fabrics can be used in the practice of thisinvention. These include, for example, cotton, hemp, rayon, regeneratedcellulose, cellulose acetate, wool, jute, polyamides, polyesters,acrylics, polyolefins, polyvinyl chloride, and polyurethane as well asmixtures of these fibers. It is generally preferred that the length ofthe fibers used in the present process be in the range of about to mm.

The binders that are applied to the fibers comprise an anionic polymerlatex and about 3 to 50 percent, and preferably 5 to 20 percent, basedon the weight of polymer in said latex, of a mixture of alkali metalsalts of disproportionated rosin and fortified rosin.

The polymer latexes that may be present in the novel binders includesolutions, emulsions, and dispersions of such polymers as acrylicresins, styrene-butadiene copolymers, polyurethanes, polyesters,polyamides, chlorinated polypropylene, polyvinyl acetate, and mixturesthereof. Particularly satisfactory results have been obtained using abinder in which the anionic polymer latex is an emulsion of an acrylicresin. As used herein, the term acrylic resin" includes a number ofpolymers prepared by the polymerization of an acrylic monomer, such asacrylic acid, methacrylic acid, ethyl acrylate, butyl acrylate,cyclohexyl acrylate, methyl methacrylate, butyl methacrylate,2-ethylhexyl methacrylate, acrylonitrile, methacrylonitrile acrylamide,methacrylamide, N-methylolacrylamide, N-methylolmethacrylamide, andmixtures thereof alone or in combination with such comonomers asstyrene, ethylene, propylene, butadiene, isoprene, chloroprene, itaconicacid and the like. illustrative of the acrylic resins that are preferredfor use in the novel binders are the following: poly (ethyl acrylate),poly (methyl methacrylate), poly (Z-ethylhexyl acrylate),polyacrylonitrile, ethyl acrylate/methacrylic acid, butylacrylate/acrylic acid, acrylonitrile/butadiene/styrene,acrylonitrile/acrylic acid/butadiene, butyl acrylate/butylmethacrylate/acrylic acid, methyl acrylate/acrylic acid/ethylene, butylacrylate/N-methylolmethacrylamide/vinyl acrylate, ethylacrylate/styrene/N- methylolacrylamide/divinylbenzene,acrylonitrile/butadiene, 2-ethylhexyl acrylate/acrylonitrile/itaconicacid, and acrylonitrile/methacrylic acid/butadiene.

The anionic polymer latexes may be formed by any suitable and convenientprocedure. For example, they may be formed by preparing a polymerizationmixture containing water, the appropriate monomers, a free-radicalpolymerization initiator, and an anionic emulsifying agent and heatingthe mixture at a temperature in the range of about to C. until thepolymerization has been completed. Among the anionic emulsifying agentsthat can be used are glycerol monostearate, sodium oleate, potassiumoleate, triethanolamine oleate, sodium lauryl sulfate, and alkyl arylsulfonates. The anionic polymer latex generally contains about 10 to 70percent by weight of the polymer. Latexes having a solids content ofabout 35 to 50 percent are ordinarily preferred.

In addition to the aforementioned components, the anionic polymer latexmay also contain defoaming agents, wetting agents, dyes, fillers, andthe like in the amounts usually used for these purposes.

The mixture of rosin salts that is present in the binders of thisinvention contains about 50 to 90 percent by weight of an alkali metalsalt of disproportionated rosin and about l0 to 50 percent by weight ofan alkali metal salt of fortified rosin. Binders that have excellentretention characteristics and that form the most satisfactory productscontain a mixture of salts that consists of 70 to 80 percent by weightof sodium, potassium, and/or lithium salts of disproportionated rosinand 20 to 30 percent by weight of sodium, potassium, and/or lithiumsalts of fortified rosin, with optimum results being obtained when themixture contains about 75 percent by weight of the potassium salt ofdisproportionated rosin and about 25 percent by weight of the potassiumsalt of fortified rosin.

The mixture of modified rosin salts may be prepared, for example, bymixing together the appropriate amounts of the individual salts.Alternatively, a mixture of disproportionated rosin and fortified rosinmay be saponified by heating it with an aqueous solution of an alkalimetal hydroxide, oxide, or carbonate, and preferably with an aqueoussolution of potassium hydroxide. If desired, the alkali metal salt ofdisproportionated rosin and the alkali metal salt of fortified rosin maybe added separately to the polymer latex to form the binding agents ofthis invention. The mixture of modified rosin salts or the individualsalts are preferably added as a dilute aqueous dispersion or solution tothe other components to form the binders.

The disproportionated rosin from which the alkali metal salt is formedmay be prepared by known procedures from wood rosin, gum rosin, or talloil rosin. For example, the rosin may be disproportionated by heating itat a temperature between and 300 C. in the presence of a catalyst, suchas palladium, platinum, nickel, iodine, sulfur, or sulfur dioxide. Asuitable method for the disproportionation of rosin is described in US.Pat. No. 2,l 38,183.

The fortified rosin that is used in the practice of this invention maybe prepared by heating rosin with about 1.9 to about 7.5 percent of itsweight of formaldehyde or a formaldehydeyielding compound, such 'asparaformaldehyde or trioxane, at a temperature between 125 and 200 C. inthe presence of an acid catalyst, such as sulfuric acid orp-toluenesulfonic acid, to form formaldehyde-rnodified rosin. Theformaldehydemodified rosin is then heated at a temperature between 160and 220 C., and preferably between 175 and 195 C., with about 4 to 12percent, and preferably 5 to 7 percent, by weight of an alpha,beta-unsaturated carboxylic acid component, such as maleic, fumaric,erotonic, acrylic, methacrylic, itaconic, citraconic, and aconiticacids, their anhydrides, their esters, and mixtures thereof.Alternatively, the fortified rosin can be prepared by heating rosin withthe appropriate amounts of an alpha, beta-unsaturated carboxylic acidcomponent at a temperature between 160 and 220 C. without theformaldehyde treatment until a product having the desired acid number isobtained.

Nonwoven fabrics may be prepared from fibers and the novel binders byprocedures that are well known in the art. The procedure is usuallycarried out in a papermaking machine or fiber mat machine that comprisesa headbox, dc watering boxes, a suction box, and a wire on which thefabric is formed. The headbox is equipped with an agitator that keepsthe fibers in suspension and that assists in the uniform distribution ofthe binder and fixing agent throughout the suspension.

1n a preferred embodiment of the invention the fibers are added to waterin the headbox to form an aqueous suspension containing about 0.005 to0.10 percent by weight of the fiber. To this suspension is added adilute aqueous solution ofa cationic fixing agent, such as a cationicureaformaldehyde resin, melamine-formaldehyde resin,dicyandiamide-formaldehyde resin, guanidine-formaldehyde resin,polyethylenimine, polyamide, or polyamidoamine resin. The amount offixing agent that is used is not critical provided that it is sufficientto precipitate substantially all of the binder that is subsequentlyadded. To the resulting suspension is slowly added a dilute aqueoussolution of the binder or, if desired, separate dilute solutions of theanionic polymer and the salts of modified rosin. In most cases about 50to 200 parts by weight of the binder is added per 100 parts by weight ofdry fibers, with about 60 to 110 parts by weight of binder per 100 partsby weight of dry fibers preferred. A few minutes after the addition ofthe binder the filtrate becomes clear, which indicates thatsubstantially all of the binder has been fixed on the fibers. The amountof water added with the binder is such that the suspension containsabout 0.05 to 1.0 gram of treated fibers per liter. The treated fibersare formed into a sheet and dried. The resulting nonwoven fabrics aresoft and flexible and have excellent tensile strength.

In another preferred embodiment of the invention, the dilute aqueousbinder solution is added to the aqueous suspension of fibers prior tothe addition of the cationic fixing agent.

The invention is further illustrated by the examples that follow. inthese examples all parts and percentages are parts by weight andpercentages by weight.

EXAMPLE 1 A mixture of modified rosin salts was prepared by thefollowing procedure;

A. Fortified rosin was prepared by heating a mixture of 90 parts ofrosin, 9 parts of maleic anhydride, and 1.7 parts of paraformaldehyde atl 75-180 C. for 90 minutes.

B. Disproportionated rosin was prepared by heating rosin at 250-310 C.for about 5 hours in the presence ofa 5 per cent palladium-on-carboncatalyst.

C. To a mixture of 345 parts of disproportionated rosin and l parts offortified rosin was added 70 parts of potassium hydroxide. The resultingmixture contained 75 percent by weight of the potassium salt ofdisproportionated rosin and percent by weight of the potassium salt offortified rosin.

EXAMPLE 2 A. A suspension of parts (dry weight) of polyester fibers inabout 500,000 parts of water was prepared. To this suspension which wasvigorously agitated was added a dilute aqueous solution that contained4.8 parts of at cationic urea-formaldehyde resin. To the resultingsuspension was slowly added a dilute aqueous dispersion that contained(a) 60 parts of an anionic polymer latex that was an anionic emulsionthat contained 50 percent of poly (ethyl acrylate) and (b) 3 parts ofthe product of Example 1. About 10 minutes after the dispersion had beenadded, the filtrate was clear. The treated fibers were formed into asheet and dried. The resulting nonwoven fabric, which was soft andresilient, had a tensile strength of 210 kg.

B. In a comparative experiment, the above procedure was followed exceptthat the product of Example 1 was not added to the dispersion thatcontained the poly (ethyl acrylate). The resulting nonwoven fabric had atensile strength of 40 kg.

C. In a comparative experiment, the potassium salt of disproportionatedrosin was used in place of the product of Example I. The tensilestrength of the resulting nonwoven fabric was kg.

EXAMPLE 3 To dilute aqueous suspension containing 100 parts (dry weight)of polyamide fibers was added a dilute aqueous solution that contained4.8 parts of a cationic urea-formaldehyde resin. To the resultingsuspension was slowly added a dilute aqueous dispersion that contained(a) 100 parts of an anionic polymer latex that contained 50 percent of apolymer of 94 percent of n-butyl acrylate, 5 percent ofN-methylolacrylamide, and 1 percent of vinyl acrylate and (b) 5 parts ofthe product of Example 1. About 10 minutes after the dispersion had beenadded, the filtrate was clear. The treated fibers were formed into asheet and dried. The resulting nonwoven fabric was soft and hadexcellent wet strength and dry strength.

EXAMPLE 4 To a dilute aqueous suspension containing 100 parts (dryweight) of polyurethane fibers was added a dilute aqueous dispersionthat contained (a) 80 parts of an anionic polymer latex that contained35 percent of poly (propyl acrylate) and (b) 2 parts of the product ofExample 1 To the resulting slurry was added a dilute aqueous solutioncontaining 5 parts ofa cationic polyamidoamine resin. The treated fiberswere formed into a sheet and dried. The resulting nonwoven fabric wassoft and resilient, and it had excellent wet strength and dry strength.

The terms and expressions that have been used are as terms ofdescription and not of limitation. There is no intention in the use ofsuch terms and expressions of excluding any equivalents of the featuresshown and described or portions thereof. It is recognized that variousmodifications are possible within the scope of the invention claimed.

What is claimed is:

1. A nonwoven fabric comprising a web of fibers bonded with a binderthat comprises (a) a polymer latex, said latex containing about 10 to 70percent by weight of a polymer selected from the group consisting ofacrylic resins, styrenebutadiene polymers, polyurethanes, polyesters,polyamides, chlorinated polypropylenes, polyvinyl acetate, and mixturesthereof and (b) 3 to 50 percent, based on the weight of polymer in saidlatex, of a mixture of rosin salts, said mixture containing about 50 to90 percent by weight of an alkali metal salt of disproportionated rosinand about 10 to 50 percent by weight of an alkali metal salt offortified rosin, said fortified rosin being the product obtained byheating rosin or formaldehyde-modified rosin and about 4 to 12 percentby weight of an alpha, beta-unsaturated carboxylic acid component at atemperature in the range of to 220 C.

2. A nonwoven fabric as set forth in claim I wherein polymer in thelatex is an acrylic resin.

3. A nonwoven fabric as set forth in claim 1 wherein the binder contains5 to percent, based on the weight of polymer in the binder, of saidmixture of rosin salts.

4. A nonwoven fabric as set forth in claim 1 wherein the mixture ofrosin salts contains 70 to 80 percent by weight of an alkali metal saltof disproportionated rosin and 20 to 30 percent by weight of an alkalimetal salt of fortified rosin.

5. A nonwoven fabric as set forth in claim 1 wherein the mixture ofrosin salts contains about 75 percent by weight of the potassium salt ofdisproportionated rosin and about percent by weight of the potassiumsalt of fortified rosin.

6. A binder for nonwoven fabrics comprising (a) a polymer latex, saidlatex containing about 10 to 70 percent by weight of a polymer selectedfrom the group consisting of acrylic resins, styrene-butadiene polymers,polyurethanes, polyesters, polyamides, chlorinated polypropylenes,polyvinyl acetate, and mixtures thereof and (b) 3 to 50 percent, basedon the weight of polymer in said latex, of a mixture of rosin salts,said mixture containing about 50 to 90 percent by weight of an alkalimetal salt of disproportionated rosin and about 10 to 50 percent byweight of an alkali metal salt of fortified rosin, said fortified rosinbeing the product obtained by heating rosin or formaldehyde-modifiedrosin and about 4 to 12 percent by weight of an alpha, beta-unsaturatedcarboxylic acid component at a temperature in the range of 160 to 220 C.

7. A binder for nonwoven fibers as set forth in claim 6 wherein thepolymer latex is an anionic emulsion containing 35 to 50 percent byweight of an acrylic resin.

8. A binder for nonwoven fabrics as set forth in claim 6 wherein thepolymer latex is an anionic emulsion containing about 50 percent byweight of poly (ethyl acrylate).

9. A binder for nonwoven fabrics as set forth in claim 6 that contains 5to 20 percent, based on the weight of polymer in the binder, of saidmixture of rosin salts.

10. A binder for nonwoven fabrics as set forth in claim 6 wherein themixture of rosin salts contains 70 to percent by weight of the potassiumsalt of disproportionated rosin and 20 to 30 percent by weight of thepotassium salt of fortified rosin.

11. In the process for the production of nonwoven fabrics wherein adilute aqueous suspension of fibers is formed, a binder comprising apolymer is added to said suspension. the polymer is precipitated ontosaid fibers, and the treated fibers are formed into a sheet and dried,the improvement that comprises incorporating in said binder 3 to 50percent, based on the weight of polymer in said binder, of a mixture ofrosin salts containing about 50 to percent by weight of an alkali metalsalt of disproportionated rosin and about 10 to 50 percent by weight ofan alkali metal salt of fortified rosin, said fortified rosin being theproduct obtained by heating rosin or formaldehyde-modified rosin andabout 4 to 12 percent by weight of an alpha, beta-unsaturated carboxylicacid component at a temperature in the range of to 220 C.

12. The process of claim 11 wherein 5 to 20 percent, based on the weightof polymer in the binder, of said mixture of rosin salts is incorporatedinto the binder.

13. The process of claim 11 wherein the mixture of rosin salts contains70 to 80 percent by weight of an alkali metal salt of disproportionatedrosin and 20 to 30 percent by weight of an alkali metal salt offortified rosin.

14. The process of claim 11 wherein the mixture of rosin salts containsabout 75 percent by weight of the potassium salt of disproportionatedrosin and about 25 percent by weight of the potassium salt of fortifiedrosin.

2. A nonwoven fabric as set forth in claim 1 wherein polymer in thelatex is an acrylic resin.
 3. A nonwoven fabric as set forth in claim 1wherein the binder contains 5 to 20 percent, based on the weight ofpolymer in the binder, of said mixture of rosin salts.
 4. A nonwovenfabric as set forth in claim 1 wherein the mixture of rosin saltscontains 70 to 80 percent by weight of an alkali metal salt ofdisproportionated rosin and 20 to 30 percent by weight of an alkalimetal salt of fortified rosin.
 5. A nonwoven fabric as set forth inclaim 1 wherein the mixture of rosin salts contains about 75 percent byweight of the potassium salt of disproportionated rosin and about 25percent by weight of the potassium salt of fortified rosin.
 6. A binderfor nonwoven fabrics comprising (a) a polymer latex, said latexcontaining about 10 to 70 percent by weight of a polymer selected fromthe group consisting of acrylic resins, styrene-butadiene polymers,polyurethanes, polyesters, polyamides, chlorinated polypropylenes,polyvinyl acetate, and mixtures thereof and (b) 3 to 50 percent, basedon the weight of polymer in said latex, of a mixture of rosin salts,said mixture containing about 50 to 90 percent by weight of an alkalimetal salt of disproportionated rosin and about 10 to 50 percent byweight of an alkali metal salt of fortified rosin, said fortified rosinbeing the product obtained by heating rosin or formaldehyde-modifiedrosin and about 4 to 12 percent by weight of an alpha, beta-unsaturatedcarboxylic acid component at a temperature in the range of 160* to 220*C.
 7. A binder for nonwoven fibers as set forth in claim 6 wherein thepolymer latex is an anionic emulsion containing 35 to 50 percent byweight of an acrylic resin.
 8. A binder for nonwoven fabrics as setforth in claim 6 wherein the polymer latex is an anionic emulsioncontaining about 50 percent by weight of poly (ethyl acrylate).
 9. Abinder for nonwoven fabrics as set forth in claim 6 that contains 5 to20 percent, based on the weight of polymer in the binder, of saidmixture of rosin salts.
 10. A binder for nonwoven fabrics as set forthin claim 6 wherein the mixture of rosin salts contains 70 to 80 percentby weight of the potassium salt of disproportionated rosin and 20 to 30percent by weight of the potassium salt of fortified rosin.
 11. In theprocess for the production of nonwoven fabrics wherein a dilute aqueoussuspension of fibers is formed, a binder comprising a polymer is addedto said suspension, the polymer is precipitated onto said fibers, andthe treated fibers are formed into a sheet and dried, the improvementthat comprises incorporating in said binder 3 to 50 percent, based onthe weight of polymer in said binder, of a mixture of rosin saltscontaining about 50 to 90 percent by weight of an alkali metal salt ofdisproportionated rosin and about 10 to 50 percent by weight of analkali metal salt of fortified rosin, said fortified rosin being theproduct obtained by heating rosin or formaldehyde-modified rosin andabout 4 to 12 percent by weight of an alpha, beta-unsaturated carboxylicacid component at a temperature in the range of 160* to 220* C.
 12. Theprocess of claim 11 wherein 5 to 20 percent, based on the weight ofpolymer in the binder, of said mixture of rosin salts is incorporatedinto the binder.
 13. The process of claim 11 wherein the mixture ofrosin salts contains 70 to 80 percent by weight of an alkali metal saltof disproportionated rosin and 20 to 30 percent by weight of an alkalimetal salt of fortified rosin.
 14. The process of claim 11 wherein themixture of rosin salts contains about 75 percent by weight of thepotassium salt of disproportionated rosin and about 25 percent by weightof the potassium salt of fortified rosin.